The invention relates to a rotary pump with a pump housing that has an intake opening and a discharge opening that are connected to each other by means of a flow space arranged within the pump housing; an impeller wheel that is arranged in the flow space and can be driven in rotation; a spiral casing that surrounds the outer circumference of the impeller wheel; and an expansion body that is in fluidic communication with the flow space.
DE 103 31 602 A1 discloses a rotary pump provided with one or several expansion bodies in order to protect the shaft of the impeller wheel from frost damage. When the volume of the water contained in the flow space changes as a result of a temperature-caused phase change of the state of aggregation, the expansion body can change its form in a flexible way. In particular, bending forces and pressure acting on the pump housing or pump components when water freezes can be avoided when the expansion body is compressed as a result of increasing pressure in the pump housing and, in this way, the volume increase of the water can be compensated in the pump housing. For producing the expansion body, flexible and elastic materials can be employed, for example, rubber bladders, closed-pore foams of a flexible material, and the like.
A rotary pump is a fluid flow machine which, by means of a rotating impeller wheel, uses centrifugal force for conveying liquids. Liquid that enters the rotary pump through an intake socket is entrained by the rotating impeller wheel and first is forced on a circular path in outward direction. Accordingly, the liquid that is contained within the impeller wheel and entrained by the impeller wheel is caused to move and new liquid is sucked into the active area of the impeller wheel. When the flow of water through the rotary pump is impaired by installed parts, the degree of efficiency of the rotary pump is decreased.
In practice, it has been found to be difficult to integrate an expansion body into the pump housing without simultaneously decreasing the degree of efficiency of the pump. While it is possible to arrange the expansion body in the motor housing car, it is a problem that the motor housing must be as seal-tight as possible in order to prevent undesirable water entry with total loss of the motor. Therefore, it is advantageous to keep, if possible, the water away from the motor housing entirely and to dispose the expansion body in the pump housing. In the pump housing, the expansion body can however impair the water passage when it is not arranged optimally. Also, manufacture of a rotary pump of the aforementioned kind should be as inexpensive as possible without significant technical expenditure.